1. Field of the Invention
The invention relates in general to circuit interrupters or circuit breakers, and more specifically to arrangements for simultaneously operating a pair of multiple pole circuit breakers in synchronism.
2. Description of the Prior Art
It is common to protect oil-filled electrical distribution transformers against secondary short circuits and sustained heavy overloads by a secondary circuit breaker mounted under oil in the transformer tank. The bimetal of the circuit breaker is responsive to both current magnitude and oil temperature, thus protecting the transformer from sustained overloads, as well as excessive current. A magnetic trip may be used to instantaneously trip the circuit breaker in response to a short circuit condition.
Relatively low cost, high quality circuit breakers are available for transformer ratings up through 100 kVA, single phase at 240/120 volt secondary voltages. Occasionally there is a need for such secondary protection on transformers, both single phase and three phase, above 100 kVA. There is little incentive to develop oil circuit breakers of this rating for transformer use, however, because of the high development and tooling costs and the relatively low volume of transformers rated above 100 kVA requiring internal circuit breakers.
Two of the standard transformer circuit breakers connected in parallel would double the presently available maximum rating. While this is easy to accomplish electrically, successful parallel operation requires that the poles of both circuit breakers open and close simultaneously.